1. Field of the Invention
The present invention relates to an information processing system and apparatus and, more particularly, to an image information processing system and apparatus suitable for a display device using a ferro-electric liquid crystal.
2. Related Background Art
A typical conventional computer terminal display device is a refresh scan type CRT. A vector scan type CRT having a partial memory function is often used for a CAD large, high-precision display. In a vector scan type CRT, once information is displayed on its screen, the screen is not updated until the screen content is erased. Therefore, the vector scan type CRT is not suitable as a real-time man-machine interface display device for performing a cursor shift display, a shift display of an icon such as a mouse as a display of information from a pointing device, an edit display (e.g., insertion, deletion, shift, and copy) of characters and sentences. On the other hand, the refresh scan type CRT requires a refresh cycle of 60 Hz or more as a frame frequency in order to prevent flickering. In order to improve icon readability and a shift display (mouse or cursor) of intrascreen information, a non-interlaced scan scheme is employed((a television receiver has a field frequency of 60 Hz or a frame frequency of 30 Hz in order to achieve a dynamic image display and simplify a drive control system). For this reason, when a display resolution is increased, the display device becomes large in size. In addition, a high power is required, and a drive controller becomes bulky, resulting in high cost.
In recent years, a flat display panel has been introduced to cope with inconvenience of a large, high-power CRT.
Several existing drive schemes are available for the flat display panels. For example, a time-divisional drive system (STN) for a twisted nematic liquid crystal, a monochromatic display system (NTN) as its modification, or a plasma display system employs the same image data transfer scheme as the CRT. In addition, a screen update scheme also employs a non-interlaced scan scheme having a frame frequency of 60 Hz or more. Therefore, the total number of scan lines constituting one frame ranges from 400 to 480, which cannot exceed 1,000 due to the following reason. Since such a display panel does not have a memory function due to the principle of driving, it requires a refresh cycle having a frame frequency of 60 Hz or more to prevent flickering. One horizontal scan interval becomes as short as 10 to 50 .mu.sec or less. As a result, a high contrast level cannot be obtained.
A ferro-electric liquid crystal display device has a larger screen than that of the above display devices and can perform high-precision display. However, in order to cope with the man-machine interface display device at a low frame frequency, a partial update scan scheme (i.e., only scan lines within an update area are scanned) is required. The partial update scan scheme is described in U.S. Pat. No. 4,655,561 to Kanbe et al.
The partial update scan scheme is particularly suitable for the ferro-electric liquid crystal display device to perform a shift display of a mouse or cursor and a scroll display of a multi window. However, partial update scan of different areas cannot be simultaneously performed. When partial update scan is performed by designating a partial update scan start address and its end address, the shift display of a mouse or cursor cannot be performed during scrolling of the multi-window. A window scroll display and a point device display are considered as examples, and their display movements are assumed. Even if the point device is moved after the scroll partial update scan is started on the display panel, update scan of the pointing device cannot be started until the end of scan of the final scan line address of the window. For this reason, the pointing device is discontinuously moved in accordance with the size of the window (i.e., the number of partial update scan lines), resulting in an unnatural shift display.